Willrich Precision Instrument Company (United States) - A dial bore gage is an instrument that measures the inner diameter of small holes. Bore gages are critical when it comes to measuring parts that have small holes in them. Typically, these versatile instruments are used as part of a quality control process to ensure that bore sizes are standardized. The dial bore gage is usually calibrated in 0.001 inches and consists of a shaft with a dial indicator situated at the top. The instrument also has an actuating plunger and the readings that it gives are usually compared to standardized measurements for analysis.

How They Work:

Dial bore gages have a contact needle that lies in the head of the dial gage. When the instrument is moved (such as when taking measurements), the needle moves and transfers data to the readout or dial. Dial bore gages also have an interchangeable end that helps to set the nominal size. Dial gage operators have to set the gage to its nominal value before commencing any measurements. Here then are some tips on how to read a dial bore gage when taking measurements of a bore or cylinder.

How to Take Accurate Measurements:

When taking measurements, you start by placing the bore gage in the micrometer and rotate the dial till the pointer is aligned to the zero marking on the dial face. One then places the dial gauge in the hole or cylinder being measured. One must take special care to ensure that the anvils on the instruments touch the sides of the hole or cylinder. Once this is done, the instrument operator then rocks the gage back and forth ensuring that the anvils do not lose contact with the walls of the cylinder. When this is done, the pointer will swing counterclockwise or clockwise. After a while, the pointer will start to move in the opposite direction toward zero. The machinist then records the precise measurement when the pointer starts heading towards zero.

Calculating the Measurements:

This is done by simply taking the measurement at the point when the needle started to reverse itself and subtracting (or adding) the measurement the instrument is calibrated to. For example, let us assume that the instrument was calibrated to 2 inches and the instrument needle changed direction at 0.007 clockwise. The measurement of the bore in question would thus be 2.007. This is because when the needle moves clockwise, you add the two numbers. Alternatively, if it had moved anti-clockwise, we would have subtracted 0.007 from 2 inches to give us 1.993.

Advantages of Dial Bore Gages:

Dial bore gages are popular with quality control operators because they are highly portable and easy to use. They also have very few moving parts and thus far less prone to breaking down than most other precision instruments. Dial bore gages also do not require sophisticated knowledge of instruments and therefore can be handled by line workers on the shop floor without much prior training.

For the best in precision instruments, get in touch with Willrich Precision. We have over 45 years of experience in delivering gaging and metrology type products to customers all over the United States.